Transmitter for interleaved error correction coded data on a transmission frame

Abstract: An error-correcting transmitter and a corresponding method are described comprising means for encoding, generating and storing in a memory the input data and an error-correcting block code having check symbols, and comprising a cell compose means for composing and transmitting a transmission cell by collecting one data block from each frame in a slanted direction with an error frame direction.

Description: BACKGROUND OF THE INVENTION' Field of The Invention The present invention relates to the transmitter and a method for coding error correction codes on the transmission frame which transmit data in the unit of cells (packets) in Asynchronous Transfer Mode. It may especially generate burst errors caused by cell loss, adding to random errors. Description of the Related Art Conventionally, the transmitter and receiver for coding error correction codes in which random errors and burst errors may occur uses interleave methods. Symbols are set in two dimensional direction, which are the direction of transmission, and the orthogonal direction of transmission: Error correction codes are generated to the orthogonal direction of transmission. Fig. 11 shows a transmission frame composed of cells which applies interleave methods. The interleave methods are described in page 220 " Hugo-riron (Code Theory) " written by Hideki Imai published by The Institute of Electronics Information and a Communication Engineers (Heisei 2). L data cells 1 are composed of N data symbols, in Fig. 11. K check cells 2 are composed of N check symbols. The transmission frame has L data cells and K check cells. The transmission frame comprising (L + K) cells uses interleave method. Input data are set at A point in the upper left of the transmission frame to B direction and are set at C point to the direction of numeral 3 and ends at D point in the right below direction. The operation is explained as follows. In Fig. 11, error correcting coding is carried out from L symbols in every data cell to the orthogonal direction of transmission, that is, the horizontal direction (the X direction in Fig. 11). Then, K check symbols are generated and stored in K check cells 2. The transmission frame is transmitted in cell units to the Y direction (the vertical direction), in Fig. 11. Assuming that error correction codes are Read Solomon codes having a frame length for error correction of (L + k) symbols and K check symbols, errors of K/2 symbols (Omit fractions) can be corrected in the X direction. A maximum loss of K cells caused by transmission noise or congestion of network can be decoded, if the location of the lost data cells is identified. The transmission frame includes data in an information field 42 between an information of header 41 and an information of trailer 43 as shown in Fig. 10. Problems to be Solved by the Invention As has been described in the related art, the conventional transmission frame composed of cells uses interleave methods in units of symbols for the error correcting coding. In order to correct errors effectively, it is necessary to set the length of (L + K) symbols for the transmission frame relatively long and transmit the frame after data of L cells is buffered. Decoding is carried out after all (L + K) cells are received. Therefore, in case slow-speed transmission is performed, the conventional art contains the problem of transmission delay being increased. In addition, it has also no way of finding the location of the cell loss. It has also insufficient efficiency in coding because coding is done symbol by symbol. US 4 649 542 discloses a method of transmitting a digital signal in the form of successive signal frames containing codes for detecting and correcting errors of the digital signal. Parity words for detecting and correcting code errors are added to every group of a predetermined number of information symbols through an interleave procedure before being transmitted. The method includes the steps of applying a first frame of symbols, taken one from each input channel, and having a first arrangement state, to a first error-correcting code encoder to generate a series of first parity words; delaying each of the symbols in the first frame and each of the first parity words by a respective different delay time in unit of the sample word at a delay line to provide a resulting second frame of symbols in a second arrangement state; applying the second frame of symbols to a second error-correction code encoder to generate a series of second parity words; and transmitting said second frame of symbols together with said second parity words. SUMMARY OF THE INVENTION It is the object of the present invention to provide an apparatus and a method which can maintain an effective error correcting ability for both random errors and burst errors caused by cell loss, symbol loss or symbol change. According to a first aspect of the present invention an error correcting transmitter having L x p information amount of input data and having an error-correcting encoding amount of k x p on error-correcting encoding the input data, wherein L, p and k are integers of at least 2, comprises an encoding means for error-correcting encoding the input data at each symbol length of L and generating an error-correcting code having check symbol length of k; and a memory for storing an error-correction code having symbol length N (= L + k) including the input data having symbol length of L and the error-correcting code having check symbol length of k; which error correcting transmitter is characterized by a cell compose means for composing and transmitting a transmission cell by collecting one data block from each frame in a slanted direction with respect to the error correction direction of the frames, the one data block obtained by division from N symbols by p. According to a second aspect of the present invention a method for error correcting transmitting having L x p information amount of input data and having an error-correcting encoding amount of k x p on error-correcting encoding the input data, wherein L, p and k are integers of at least 2, comprising storing an error-correction code having symbol length N (= L + k) including the input data having symbol length of L and the error-correcting code having check symbol length of k; and error-correcting encoding the input data at each symbol length of L and generating an error-correcting code having check symbol length of k; is characterized by composing and transmitting a transmission cell by collecting one data block from each frame in a slanted direction with respect to the error correction direction of the frames, the one data block obtained by division from N symbols by p. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, Fig. 1 shows a block diagram of a transmitter for coding error correction codes, according to an embodiment which is useful to explain the present invention, but does not illustrate the invention; Fig. 2 shows a configuration of the transmission frame according to the embodiment of Fig. 1; Fig. 3 shows a block diagram of a transmitter for coding error correction codes on the transmission frame according to another embodiment which is useful to explain the present invention, but does not illustrate the invention; Fig. 4 shows an explanatory view of the transmission frame in which one cell is divided into p block data according to the embodiment of Fig. 3; Fig. 5 shows a block diagram of a transmitter for coding error correction codes on the transmission frame according to a further embodiment which is useful to explain the present invention, but does not illustrate the invention; Fig. 6 shows an explanatory view of the transmission frame of the embodiment of Fig. 5; Fig. 7 shows an array of the block data stored in the second buffer memory according to the embodiment of Fig. 5; Fig. 8 shows a configuration of the frame for error-correction after changing the position of identifiers in Fig. 7; Fig. 9 shows an explanatory view of the transmission frame of an embodiment of the present invention; Fig. 10 shows the general configuration of the transmission cell of the related art; and Fig. 11 shows the relationship between the transmission frame and interleave method according to the related art. DESCRIPTION OF THE EMBODIMENTS Fig. 1 shows an embodiment of the transmitter for coding error correction codes on the transmission frame based on the present invention. In the figure, an error correcting encoder 4 generates error correction codes having a frame length for error correction of (L + K) symbols and error correction length of K symbols; a register 51 temporarily stores data of N symbols; a buffer memory 6 stores entire input data as a transmission frame; a data distributor 7 indicates addresses of data in the buffer memory 6 transferred from the register 51; a cell composer 8 composes each transmission cell; and an input terminal 9 and an output terminal 10 transfer the data. In the present explanation, data of N x (L + k) symbols are called a transmission frame, data of N x L symbols are called information of a transmission frame, data of (L + k) symbols are called a frame for error correction, and transmission data of N symbols are called a transmission cell. The operation will now be described. Here, the error correction codes are Reed Solomon error correction codes. As described in the related art, input data are filled into the buffer memory from point A, on the upper left of the transmission frame, in the direction of point E, and from point F in the direction of numeral 3, for forming the frame. In this embodiment, the width of the horizontal direction is assumed to be N symbols, and the data of N symbols are regarded as a transmission unit. Check symbols are generated in the vertical direction, that is, the orthogonal direction of transmission. In the embodiment shown in Fig. 1, data through the input terminal 9 are temporarily stored in the register 51 in units of N symbols, then transferred to the cell composer 8 for generating the transmission cell. At the same time, the data of N symbols are transferred to the first row in the vertical direction in the buffer memory 6. The next data of N symbols are transferred to the cell composer 8 as well as to the second row in the buffer memory 6. When block data of L cells are stored in the buffer memory 6, the error correcting encoder 4 forms a frame for error correction (FEC), which refers to the buffer memory, and generates k check symbols 2. After storing the check symbols in the assigned addresses of the buffer memory 6, check symbols 2 in k frames for error correction are read out in the horizontal or transmission direction and transmitted through the cell composer 8 as the transmission cell. Thus, the apparatus shown in Fig. 1 has the advantage of the interleave methods and eliminates the transmission delay. Fig. 2 illustrates an array of block data in the buffer memory 6 as well as the configuration of the transmission frame in this embodiment. In the figure, numeral 1 shows a data cell, 2 shows a check cell. In this embodiment, error correction coding is performed in the orthogonal direction of transmission, by using L data cells and k check cells as one unit. The transmitter for coding error correction codes on the transmission frame in this embodiment generates transmission data of N symbols as well as stores data completely for coding. There is shown another embodiment of the transmitter for coding error correction codes on the transmission frame in connection with Fig. 3, which is useful for explaining the invention but does not illustrate the invention. In the figure, numerals 1 to 10 and 51 are the same elements as in Fig. 1. The input data is filled from the upper left of the transmission frame to the upper right and from the left of the next row to the right as described in the embodiment of Fig.1. A selective cell composer 81 operates as follows ; The selective cell composer 81 scans input data in the buffer memory 6 to the vertical direction by N/p symbols in the first column. Then it scans from the top of the next column by N/p symbols. Thus, the scan by every N/p symbol is repeated to the horizontal direction until a cell of N symbols is generated, as shown in dotted line in Fig. 3. The operation will now be described, referring to Fig. 3. In this embodiment, as described in the related art, the horizontal direction shows the coding direction. Data transferred from the input terminal 9 are stored in the assigned position in the buffer memory 6, temporarily. But, when data of N/p blocks in the vertical direction, that is, the transmission direction, are provided by p times, one transmission cell composed of p x (N/p) data symbols is transmitted. The error correcting encoder 4 operates in the conventional ways. The advantage of the interleave methods is preserved because the coding is performed in the orthogonal direction of transmission. In Fig. 4, there is shown the configuration of the transmission frame in this embodiment. Here, N/p is supposed to be divided by integers. One cell is composed of (N/p) data symbols in the vertical direction of buffer memory 6 in Fig. 3 being collected by p times in the coding direction. Thus, time required for starting transmission is reduced by 1/p times, comparing to the related art. In this embodiment, after data being stored in the buffer memory, transmission cells are generated selectively through the selective cell composer at the time of transmission. On the other hand, after data corresponding to the transmission cell are distributed and stored, coding can be performed in the orthogonal direction of transmission in accordance with this distribution. That is, coding is performed in every N/p data symbol which are stored in the buffer memory. In other words, it is possible to store the data blocks first in a dotted line in Fig. 3 and read out the data in a solid line for transmission. Fig. 5 illustrates a further embodiment of a transmitter for coding error correction codes on the transmission frame useful for explaining the invention, but does not illustrate the invention. In Fig. 5, 82 shows a selective cell composer which generates the transmission cell by replacing one data symbol or block with one error-correction symbol or block. Output data of a counter 30 are transferred into plural symbols or blocks of a cell in this embodiment. The operation will be described hereinafter. N data symbols are transmitted in units of divided p blocks. Symbol length N is determined to be divided by the block number p. A temporary frame is composed in units of (L + K) cells. However, cells from the (L - k + 1) th to the L th have identifiers in two different data blocks. The transmission frame shown in Fig. 6 is composed through the selective cell composer 82 by exchanging one block of check symbols with one block of data symbols which has an identifier. This embodiment is characterized in that identifier 11 is stored in an assigned position of each cell. In the transmission frame in Fig. 6, data from the first cell to the (L - K) th cell are composed of (N - n) data symbols received from the input terminal 9 and an identifier of n symbols is attached by the dividing circuit 52. The total N data symbols of each cell from the first cell to the (L - k) th cell is divided into p data blocks equally and stored in assigned addresses in the buffer memory 6. Further, each of the data cells after the (L - k + 1 ) th cell is composed of (N - 2n) symbols received from the input terminal 9 and two identifiers 11 of n symbols each are attached by the dividing circuit 52. Then, each of the cells of N data symbols is divided into p data blocks and stored in assigned addresses in the buffer memory 6. Thereafter, one of data blocks having an attached identifier 11 in the (L - k + 1) th cell to the L th cell is exchanged with the first block of the (L + 1) th cell to the (L + k) th cell. Thus, transmission cells after the replacement are shown in Fig. 6. Thereby, identifiers are incorporated into the check cells, the (L + 1) th cell to the (L + k) th cell. The operation will now be described by using numerical data in Fig. 7 and Fig. 8. Fig. 7 shows an example of the temporary frame of block data in the buffer memory 6 of this embodiment, in which N = 48, p = 12, L = 11, and k = 1. That is, there is shown the case in which p = L + k. Numeral 11 shows identifiers and 12 shows check symbols in the figure. In an array of block data shown in Fig. 7, the frame for error-correction is composed of block data in the horizontal direction. For example, block data (1 - $1, 2 - $12, 3 - $11, 4 - $10, 5 - $9, 6 - $8, 7 - $7, 8 - $6, 9 - $5, 10 - $4, 11 - $3, F - $1) composes one frame for error-correction. In Fig. 8, there is shown a configuration of the transmission frame in this embodiment. The transmission frame is composed in units of 12 cells, in which L = 11, k = 1. In the embodiments of Figs. 1 and 3, the transmission frame is composed of L data cells 1 and k check cells 2. In this embodiment, cells are regenerated by exchanging block data between data cells 1 and check cells 2 so that the identifiers 11 might be stored at the assigned positions of each cell. In Fig. 8, the identifiers 11 are appended to two data blocks of the 11th cell (11 - $1) and (11 - $3). Then, data blocks (11 - $3) and (F - $1) are exchanged between the 11th cell and the 12th check cell. In this embodiment, data composing a transmission cell are divided into plural data blocks and arranged separately on the plural frames for error correction. In case that cell loss is detected, decoding process for the lost cell is performed by correcting lost block data in each frame for error correction related to the block data in the lost cell. Therefore, in order to correct cell loss, each frame for error correction should have a capability to correct errors of the block data in the related cell if any cell is lost. For example, in order to correct loss of one block data of N/p symbols whose location is identified by using Reed Solomon Codes, data having more than N/p symbols are required for the check symbol length. And, in order to correct loss of two block data whose locations are identified by using Reed Solomon Codes, data having more than 2 N/p symbols are needed for the check symbol length when each of the block data length is N/p symbols. Further, in order to correct random errors whose location are not detected by using Reed Solomon Codes, data having more than 2 N/p symbols are required for the check symbol length for correcting errors of one block data of N/p symbols. In case that all the data block length has 2 N/p symbols and Reed Solomon Codes in which check symbol length k = 2 N/p symbols are used, it should be settled that plural block data in the related cell are not contained in each frame for.error correction to correct errors of one lost cell whose location is alreadyidentified. In an array of block data, shown in Fig. 7, as described before, a frame for error correction is composed of block data in the horizontal direction and a transmission cell is composed of block data in the vertical direction. However, because as to a check cell located on the right side in Fig. 7, the identifier 11 of the transmission cell isn't attached, cell loss detection by using the identifier 11 can't be performed. Therefore, according the present embodiment, as shown in Figs. 7 and 8, the identifiers 11 are attached on the block data "11-$3" and "11-$1" and the block data "11-$3" is replaced by the block data "F-$1". Thus, because the identifiers 11 are attached to all the cells, cell loss detection can be performed for any cell by using the identifier 11. Further, because block data "11-$3" is replaced by the block data "F-$1" in the same frame for error correction, the replacement process doesn't cause to change the error correction ability. In the present embodiment, one frame for error-correction doesn't have plural block data included in the same cell. That is, one cell doesn't have plural block data included in the same frame for error correction. It also means that each error correction frame has one data block from each data cell and error correction cell. Generally, in case of detecting one cell loss previously, at least one block data is required for the error correcting coding. If Reed Solomon error correction codes are employed to correct the loss of one block data, k check symbols not less than N/p symbols are required. Here, data can be recovered from the cell loss because one frame for error-correction has just one block data included in each cell. As shown in Fig. 7, block data (11 - $3) and (F - $1) are in one frame for error-correction. That is, one frame for error correction has just one block data of each cell. Therefore, each of the block data in check cells is replaced with one of the block data with identifiers in the transmission cell in each of the same frames for error correction. That is, the transmission cell including the data block which is replaced with the block data in.the check cell has two identifiers. Thereby, error correction coding can be performed so as to correct either random errors or cell loss, and transmission efficiency is increased. In another embodiment, the N data symbols aren't divided into p blocks. One symbol of the N data symbols is replaced by one symbol of the check symbols. A detailed explanation is omitted, for the configuration and the operation can be easily understood by referring to the description of Fig.1 in connection with Figs. 6 to 8. The transmitter for coding error correction codes on the transmission frame attaches identifiers on the top of each transmission cell and stores the data completely for coding. One of the check symbols is replaced with one of the data symbols including identifiers. Then, transmission is carried out in units of N data symbols. Fig. 9 illustrates the configuration of a transmission cell according to the present invention Fig. 9 (a) shows the relationship between data block and check symbols in one transmission frame. In this embodiment, check symbols have one data block and k symbols. And, identifiers aren't especially appended but they can be appended to the data block S1 at the end of each of the frames for error correction. Therefore, in case of composing a transmission cell, data blocks are scanned aslant as shown in Fig. 9 (a). And the transmission cell shown in Fig. 9 (b) is composed. Thus, though identifiers aren't replaced, it is possible to comprise all the facilities described in the present embodiment.

Claims: An error correcting transmitter having L x p information amount of input data and having an error-correcting encoding amount of k x p on error-correcting encoding the input data, whereby L, p and k are integers of at least 2, the error correcting transmitter comprising: an encoding means (4) for error-correcting encoding the input data at each symbol length of L and generating an error-correcting code having check symbol length of k; and a memory (51) for storing an error-correction code having symbol length N (= L + k) including the input data having symbol length of L and the error-correcting code having check symbol length of k; characterized by a cell compose means (8) for composing and transmitting a transmission cell by collecting one data block from each frame in a slanted direction with respect to the error correction direction of the frames, the one data block obtained by division from N symbols by p. A method for error correcting transmitting having L x p information amount of input data and having an error-correcting encoding amount of k x p on error-correcting encoding the input data, wherein L, p and k are integers of at least 2, comprising storing an error-correction code having symbol length N (= L + k) including the input data having symbol length of L and the error-correcting code having check symbol length of k; and error-correcting encoding the input data at each symbol length of L and generating an error-correcting code having check symbol length of k; characterized by composing and transmitting a transmission cell by collecting one data block from each frame in a slanted direction with respect to the error correction direction of the frames, the one data block obtained by division from N symbols by p.

Inventors: KATO YOSHIAKI, MATSUZAKI KAZUHIRO, MURAKAMI TOKUMICHI, YAMAGISHI ATSUHIRO, YOSHIDA HIDEO, KATO, YOSHIAKI, MATSUZAKI, KAZUHIRO, MURAKAMI, TOKUMICHI, YAMAGISHI, ATSUHIRO, YOSHIDA, HIDEO, Kato, Yoshiaki Mitsubishi Denki Kabushiki Kaisha, Matsuzaki, Kazuhiro Mitsubishi Denki Kabushiki, Murakami, Tokumichi Mitsubishi Denki Kabushiki, Yamagishi, Atsuhiro Mitsubishi Denki Kabushiki, Yoshida, Hideo Mitsubishi Denki Kabushiki Kaisha
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1994
Main classification: H03M13
IPC codes: H04L12, H03M13, H04L7, H04L1